Biological indicators and chemical indicators used to determine the efficacy of sterilization are well known in the art. It is well recognized in the art of sterilization that biological tests are the most accurate sterility tests because they provide a high level of confidence that all parameters necessary to achieve sterilization, including the interrelated parameters of time, temperature and concentrations of moisture, chemicals or radiation dose, have been reached. In conventional biological indicators, a test organism which is many times more resistant to the sterilization process employed than most organisms which would be present by natural contamination, is coated on a carrier and placed in a sterilizer along with the articles to be sterilized. After completion of the sterilization cycle, the carrier is incubated in nutrient growth medium to determine whether any of the test organism survived the sterilization procedure.
Several unitary biological indicators, i.e., indicators containing both the test microorganism and the nutrient growth medium, are described in U.S. Pat. Nos. 3,239,429; 3,440,144; 3,661,717; 4,291,122; 4,304,869; 4,416,984; 4,461,837; 4,528,268; 4,579,823; 4,580,682; 4,596,773; and 4,717,661. The sterility indicator described in U.S. Pat. No. 3,661,717, for example, is comprised of a container for a test spore strip with an opening at one end. Also in the container is an ampoule filled with an aqueous nutrient and indicator system. The container is covered with a gas transmissive, bacterial impermeable closure. In use this indicator is placed within the sterilization chamber during the cycle and sterilant enters the container displacing air in the container. Circulation of the sterilant around the spore strip kills the spores. Thereafter the ampoule containing the nutrient and indicator media is crushed upon deformation of the outer compartment and any spores remaining viable are allowed to grow in the nutrient medium. In all of the previously described conventional biological indicators the entire volume of growth medium is observed for indication of spore survival, and growth of a detectable number of microorganisms takes a minimum of twenty-four hours. During this period, the supposedly sterilized articles should be quarantined.
In frequent practice, however, the hospital has neither the space for proper quarantining of the supposedly sterilized articles, nor a sufficient number of the articles themselves to permit actual quarantining. As a result, the supposedly sterilized articles are placed back into stock on the assumption that sterilization was proper and will be confirmed by a subsequent report from the laboratory. Applicants' commonly assigned U.S. Patent entitled "Rapid Method for Determining Efficacy of a Sterilization Cycle and Rapid Read-Out Biological Indicator", (U.S. Pat. No. 5,073,488), filed of even date herewith, describes a method of determining sterilization efficacy which employs an enzyme whose activity can be correlated with the viability of at least one microorganism commonly used to monitor sterilization efficacy. The enzyme, following a sterilization cycle which is sublethal to the test microorganism, remains sufficiently active to react with an enzyme substrate in a relatively short period of time, e.g., normally eight hours or less. However, the enzyme is inactivated or appreciably reduced in activity following a sterilization cycle which is lethal to the test microorganism.
There remains a need for a biological sterility indicator which will provide even more rapid and reliable results.